US4926126A - Probehead of magnetic resonance apparatus - Google Patents
Probehead of magnetic resonance apparatus Download PDFInfo
- Publication number
- US4926126A US4926126A US07/355,025 US35502589A US4926126A US 4926126 A US4926126 A US 4926126A US 35502589 A US35502589 A US 35502589A US 4926126 A US4926126 A US 4926126A
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- US
- United States
- Prior art keywords
- probehead
- pin diodes
- transmitting
- reactance
- reactance elements
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
- G01R33/3628—Tuning/matching of the transmit/receive coil
Definitions
- the present invention relates to a probehead of a magnetic resonance (MR) apparatus used to transmit an RF field and to receive an MR signal in an MR apparatus such as an MR imaging apparatus and an MR spectroscopy apparatus.
- MR magnetic resonance
- a conventional probehead of an MR apparatus used in a medical diagnosis is arranged to have an equivalent circuit diagram shown in FIG. 1.
- This probehead comprises a transmitting coil L1, a receiving coil L2, and variable capacitors C1 to C6.
- S/N signal-to-noise
- one of the transmitting and receiving coils L1 and L2 which is currently not used must be decoupled. That is, upon transmission, the transmitting coil L1 for forming an RF field from the probehead toward an object to be examined is tuned, while the receiving coil L2 for receiving an MR signal based on an MR phenomenon of the object to be examined is decoupled.
- the transmitting coil L1 Upon reception, to the contrary to the transmission, the transmitting coil L1 is decoupled, and the receiving coil L2 is tuned.
- Such decoupling control upon transmission and reception is performed by a switching section 2A connected to each of the transmitting and receiving coils L1 and L2.
- a PIN diode is used as a switching element for performing a decoupling operation of the coils L1 and L2 at high speed.
- FIG. 2 shows a circuit of a transmitting system of a probehead using a PIN diode D.
- the transmitting circuit shown in FIG. 2 comprises RF (choke) coils RFC1 and RFC2 and a diode driver 31 in addition to the variable capacitors C1, C2, and C3, the transmitting coil L1 and the PIN diode D.
- the driver 31 includes DC bias power supplies 32 and 33 and a switch SW.
- the PIN diode D is obtained by inserting an I region (intrinsic region: an intrinsic semiconductor region having a sufficiently low impurity concentration) between a p- and n-type regions of a p-n junction diode.
- I region intrinsic region: an intrinsic semiconductor region having a sufficiently low impurity concentration
- an RF series resistance changes upon application of a forward DC bias current.
- a single PIN diode D is used in a conventional probehead as shown in FIG. 2.
- an object of the present invention to provide a probehead of an MR apparatus in which an arrangement of a switching section of the probehead is improved to effectively control decoupling of the coil to which a high RF current is supplied without degrading a function of the probehead.
- a probehead of an MR apparatus comprises transmitting and receiving coil elements for transmitting an RF magnetic field and receiving an MR signal based on an MR phenomenon induced in an object to be examined, respectively, and switching units for controlling decoupling of the transmitting and receiving coil elements, wherein at least the switching unit provided for the transmitting coil unit comprises a plurality of PIN diodes connected in parallel with each other, and reactance elements connected in series with the plurality of PIN diodes and having reactance components, absolute values of which are sufficiently larger than resistance components of the PIN diodes in an on-state.
- an absolute value of a reactance component of each of the reactance elements connected in series with the plurality of parallel PIN diodes is sufficiently larger than a resistance component of each PIN diode. Therefore, an RF current to be flowed to the switching section is divided mainly in accordance with a ratio of each reactance component and flowed to each PIN diode. As a result, an influence of variations in resistance components of the respective PIN diodes can be effectively reduced, thereby preventing destruction of the PIN diode.
- a probehead of an MR apparatus capable of handling a high RF current and achieving a stable transmission/reception switching operation can be provided.
- FIG. 1 is a basic equivalent circuit conventional probehead of an MR apparatus
- FIG. 2 is a circuit diagram showing a part of the conventional probehead in detail
- FIG. 3 is a circuit diagram showing a parallel circuit of PIN diodes
- FIG. 4 is an equivalent circuit diagram showing an embodiment of a probehead according to the present invention.
- FIG. 5 is a circuit diagram showing a switching section in the probehead shown in FIG. 4 in detail
- FIG. 6 is an equivalent circuit diagram of the switching section of the present invention shown in FIG. 5;
- FIG. 7 is an equivalent circuit diagram of a switching section shown in FIG. 3;
- FIG. 8 is a schematic view showing a part of another embodiment of the probehead according to the present invention.
- FIG. 9 is a view showing an arrangement of a switching section in the embodiment shown in FIG. 8 in detail.
- FIG. 4 equivalently shows a probehead of an MR apparatus according to an embodiment of the present invention.
- the same reference numerals as in FIG. 2 denote parts having the same functions, and a detailed description thereof will be omitted.
- the probehead shown in FIG. 4 differs from the probehead shown in FIG. 2 in that a switching section 2 is arranged as shown in FIG. 5.
- reactance elements 3-1, 3-2, ..., 3-N are connected in series with parallel PIN diodes D1, D2, ..., DN, respectively.
- the reactance elements 3-1, 3-2, ..., 3-N are arranged to satisfy the following condition assuming that resistance components of the PIN diodes D1, D2, ..., DN are RS1, RS2, ..., RSN and reactance components of the reactance elements 3-1, 3-2, ..., 3-N are jX1, jX2, ..., jXN, respectively: ##EQU1##
- the above condition (1) is satisfied when the PIN diodes are in an on-state.
- coils or conductors or conductor patterns equivalently serving as coils at the resonance frequency
- capacitors having small variations
- a maximum internal power dissipation PDmax is represented by the following equation: ##EQU3## and the following relation is established: ##EQU4## PDmax falls within the range determined by the following equation. That is, when no current-limiting reactance element is present: ##EQU5##
- the maximum internal loss PDmax' of the switching section 2 shown in FIG. 6 according to the present invention is smaller than the maximum internal power dissipation PDmax of the switching section 2A shown in FIG. 7 not including the reactance elements 3-1, ..., 3-N.
- the switching section 2 can suppress variations in an allowable RF current due to variations in resistance components RS1, ..., RSN of the PIN diodes D1, ..., DN. Therefore, the parallel PIN diodes D1, ..., DN can be stably used.
- the transmitting coil L1 of the probe head comprises band-like conductor plates as schematically shown in an expanded view of FIG. 8.
- the transmitting coil L1 comprises, e.g., band-like copper plates.
- Fixed capacitors Cc comprising, e.g., ceramic capacitors are placed at regular intervals of the transmitting coil L1 in order to decrease an apparent inductance. In this case, as shown in FIG.
- a switching section 2' for decoupling may have an arrangement in which the band-like copper plates constituting the coil L1 are partially notched to form a plurality of narrow band-like portions serving as reactances (in this case, inductances) and PIN diodes D1, D2, ..., DN are inserted therein.
- a transmitting coil has been described in the above embodiment, a receiving coil can be similarly arranged as described above.
- parallel PIN diodes are generally required for a transmitting coil for flowing a high RF current. Therefore, the PIN diodes need not be provided in parallel with each other in a receiving coil, i.e., the present invention need not be applied to a receiving coil.
Abstract
Description
Claims (7)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP63-124877 | 1988-05-24 | ||
JP63124877A JP2647139B2 (en) | 1988-05-24 | 1988-05-24 | Probe head for magnetic resonance equipment |
Publications (1)
Publication Number | Publication Date |
---|---|
US4926126A true US4926126A (en) | 1990-05-15 |
Family
ID=14896304
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US07/355,025 Expired - Lifetime US4926126A (en) | 1988-05-24 | 1989-05-22 | Probehead of magnetic resonance apparatus |
Country Status (2)
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US (1) | US4926126A (en) |
JP (1) | JP2647139B2 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5144244A (en) * | 1989-09-18 | 1992-09-01 | Siemens Aktiengesellschaft | Error-proof decoupling of transmission and reception antennas in a nuclear magnetic resonance apparatus |
NL9202194A (en) * | 1991-12-17 | 1993-07-16 | Univ California | SELF-ELIMINATING RF RECEIVER COIL, WHICH IS USED FOR DISCONNECTING MRI TRANSMITTER / RECEIVER RF COILS. |
US5903150A (en) * | 1996-06-03 | 1999-05-11 | Roznitsky; Samuel | Antenna system for NMR and MRI apparatus |
CN110794349A (en) * | 2018-08-02 | 2020-02-14 | 西门子(深圳)磁共振有限公司 | Head and neck coil, radio frequency signal processing method and magnetic resonance imaging device |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4763076A (en) * | 1987-09-01 | 1988-08-09 | The Regents Of The University Of California | MRI transmit coil disable switching via RF in/out cable |
US4820987A (en) * | 1986-12-22 | 1989-04-11 | U.S. Philips Corporation | Magnetic resonance imaging apparatus comprising an activatable birdcage RF coil |
US4855680A (en) * | 1987-11-02 | 1989-08-08 | The Regents Of The University Of California | Enhanced decoupling of MRI RF coil pairs during RF tuning of MRI RF transmit coil |
-
1988
- 1988-05-24 JP JP63124877A patent/JP2647139B2/en not_active Expired - Lifetime
-
1989
- 1989-05-22 US US07/355,025 patent/US4926126A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4820987A (en) * | 1986-12-22 | 1989-04-11 | U.S. Philips Corporation | Magnetic resonance imaging apparatus comprising an activatable birdcage RF coil |
US4763076A (en) * | 1987-09-01 | 1988-08-09 | The Regents Of The University Of California | MRI transmit coil disable switching via RF in/out cable |
US4855680A (en) * | 1987-11-02 | 1989-08-08 | The Regents Of The University Of California | Enhanced decoupling of MRI RF coil pairs during RF tuning of MRI RF transmit coil |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5144244A (en) * | 1989-09-18 | 1992-09-01 | Siemens Aktiengesellschaft | Error-proof decoupling of transmission and reception antennas in a nuclear magnetic resonance apparatus |
NL9202194A (en) * | 1991-12-17 | 1993-07-16 | Univ California | SELF-ELIMINATING RF RECEIVER COIL, WHICH IS USED FOR DISCONNECTING MRI TRANSMITTER / RECEIVER RF COILS. |
US5903150A (en) * | 1996-06-03 | 1999-05-11 | Roznitsky; Samuel | Antenna system for NMR and MRI apparatus |
CN110794349A (en) * | 2018-08-02 | 2020-02-14 | 西门子(深圳)磁共振有限公司 | Head and neck coil, radio frequency signal processing method and magnetic resonance imaging device |
CN110794349B (en) * | 2018-08-02 | 2022-05-20 | 西门子(深圳)磁共振有限公司 | Head and neck coil, radio frequency signal processing method and magnetic resonance imaging device |
Also Published As
Publication number | Publication date |
---|---|
JP2647139B2 (en) | 1997-08-27 |
JPH01293860A (en) | 1989-11-27 |
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